The present invention relates to a sheet size determining apparatus, and more particularly it relates to a sheet size determining apparatus for use in an image forming apparatus having sheet containers which contain sheets of different sizes.
One class of copying machines has the capacity to copy onto A3 size sheets wherein the sheets of copy paper are transported widthwise from a tier of sheet drawers, each of which contains a different size of sheet and can be drawn out from the copying machine body. The sheets are normally transported in their sheet width direction in such a copying machine, and sensors for detecting sheet size provided in the sheet drawers only detect the sheet dimension in the direction perpendicular to the transportation direction, i.e., in the direction of the machine depth. This is because sheets of all ordinarily required sizes can be transported in the sheet width direction in a copying machine which is capable of handling A3 size sheets, making it unnecessary to transport sheets in their sheet length direction. Furthermore, copying speed is expedited by transportation of the sheets in the sheet width direction as opposed to the sheet length direction.
Problems may arise in the forgoing copying machine when it is used in combination with an automatic original feeder and operated in a mixed-size mode. The mixed size mode therein is for handling a stack of originals containing, for example, A3- and A4-size originals.
No difficulties arise if the A3- and A4-size originals in such a stack handled in the mixed-size mode are arranged such that transportation by the automatic original feeder is in the width direction of the sheets of both sizes. However, a stack containing originals previously bound by a stapler or having punch-holes can create handling problems, if in such a case the stack includes A4-size originals situated such that their lengthwise dimension is coincident with the widthwise dimension of the A3-size originals in the direction of transport.
As explained, the sheet drawers, provided for supplying sheets to the image forming part of the copying machine, have sensors which detect copy paper sheet dimension only in the direction of the machine depth. Wherein a mixed stack of originals of A3 and A4 size as above is set into the automatic original feeder in the mixed size mode, A3- and A4-size sheets of copy paper are so placed into respective sheet drawers as to be correspondingly oriented to the originals. However, the apparatus then cannot distinguish, by its machine depthward dimension-detecting sensors, A4- from A5-size sheets, since the widthwise dimension of the former corresponds to the lengthwise dimension of the latter, A5-size sheets.
Although additional sensors could be provided in order to determine whether the sheets to be transported from a sheet drawer are located widthwise or lengthwise, the added structural complexity would increase manufacturing costs.